It is known in the prior art to change an input fluctuating DC voltage into an isolated and regulated DC output voltage through respective thyristor switches by alternately charging and discharging a capacitor through a transformer. Each time an alternate thyristor is turned ON, the capacitor is either charged or discharged. Voltage sloping circuits have been used to reduce the rate of rise of the voltage applied to each one of the thyristors when the other thyristor is turned ON, which circuits in conjunction with the leakage reactance of the transformer provide a filter to change the voltage step function generated when one thyristor turns ON to a much slower voltage rise time on the other thyristor.